Patent GB-1359167-A (GB)
Title: Glass articles having protected edge portions
IPC: C03C27/12
Filed: 1971-05-21
Abstract: 1359167 Protecting edges of glass laminates GLAVERBEL 21 May 1971 16284/71 Heading B5N [Also in Division C1] An article having an edge portion of glass or glass-ceramic containing compressive surface stresses due to chemical tempering has a protective covering or coverings adhered thereto and comprising fibre reinforced plastics material or one or more plastics coated or plastics impregnated filaments or rovings. The articles may be plane or curved glass sheets, glass laminated panels, plane or curved, or containers such as flower bowls. As shown, a sheet 35, Fig. 2, is provided with two rovings 36 of fibres of E type glass impregnated with phenoxyl resin and secured to the edge by a neoprene-based adhesive layer 37. In Fig. 3, two sheets 39, 40 joined by a sheet 38 of polyvinylbutyral have two glass-fibre plastics impregnated rovings 41 secured direct to the edges of the sheets by fusing to the layer 38. A layer, similar to layer 37 may also be used. In addition to the chemical tempering, which may be effected only on the edges by protecting the remaining areas with paraffin wax, the article edges may be abraded, particularly to give the edge a flat bevelled profile, and the glass edges may be treated to reduce the impairment of the surface, as by a fluorine-containing agent such as an aqueous solution of hydrofluoric acid alone or with sulphuric acid. The sheets may also be thermally tempered. Chemical tempering is preferably by molten salt contacting medium, but a gas, a paste or a vapour may be used and, for sodium containing glass, the sodium ion may be replaced by larger ions, as potassium, or smaller, lithium, ions. In examples, for a lithium containing glass, a mixture of NaCl and MgCl 2  or of NaCl and AlCl 3 , the latter being followed by a bath of KNO 3  with acid treatment both before and after. For an alumino-silicate glass a bath of LiNO 3 + NaCl; for soda-lime glass a bath of KNO 3  alone; with K 2 CO 3  or with CO 2  gas passed through. Alternatively, a sheet in KNO 3  was removed immediately to leave a coating film which was then irradiated with infra-red irradiation to heat the inner layers of the sheet, the surface layers being maintained below 490 C. by blowing air, the sheet then being rapidly cooled and washed to effect both chemical and thermal tempering. In addition to glass fibres or rovings, nylon fibres may be used. A larger variety of suitable plastics material is given including polyesters, phenol formaldehyde and elastomer plastics such as silicone or elastomers vulcanized in situ. Thermoplastics suggested include cellulose propionate, polyvinyl chloroacetate, polyvinyl acetate or polyethylene or elastomers such as acrylonitrile styrene copolymers. Combinations of polymers such as acrylonitrile-butadienestyrene/polyvinyl chloride. Phenoxy resins may be used. A continuous process is disclosed for plastics impregnated or coated threads or rovings in which the roving is passed through a solution of the thermoplastic and dried by heating. The coated roving is then applied to the edge by a hot air welding gun (46) having a guide ring (51) for the roving (43) and guide sheath (49) which has a pressing shoe (45) to press the roving (43) on to the edge of a glass panel (44). Specifications referred to are 1,274,731, 1,359,165 and 1,358,061.